Diagnostic apparatus and diagnostic method for fuel cell

ABSTRACT

According to an aspect of the invention, a diagnostic apparatus which diagnoses a state of the fuel cell includes an operation device which is used for operating the fuel cell; an operational state detecting portion which detects a change in an operational state of the fuel cell; a device control portion which controls the operation device such that the fuel cell is operated according to at least one predetermined operation pattern; and a diagnostic portion which diagnoses the state of the fuel cell based on the change in the operational state of the fuel cell that is detected by the change in the operational state detecting portion when the fuel cell is operated by the device control portion according to the at least one predetermined operation pattern, and the at least one predetermined operation pattern.

INCORPORATION BY REFERENCE

[0001] The disclosure of Japanese Patent Application No. 2002-344416filed on Nov. 27, 2002 including the specification, drawings andabstract is incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The invention relates to a diagnostic apparatus and a diagnosticmethod for a fuel cell and, more particularly, to a diagnostic apparatusand a diagnostic method for diagnosing a state of a fuel cell.

[0004] 2. Description of the Related Art

[0005] Heretofore, there has been proposed a fuel cell system of thistype which makes a determination on an abnormal operational state suchas excessiveness or scarceness of water contained in a fuel cell stack(e.g., Japanese Patent Application Laid-Open No. 9-245826 (FIG. 1, FIG.2)). In this system, time-dependent change patterns of a voltage in acell or a cell block constituting the fuel cell stack are measured andstored in advance as to various operational conditions, and adetermination on an operational state of the fuel cell stack is made bycomparing an actual time-dependent pattern with the stored patterns.

[0006] In such a fuel cell system, an abnormality of the fuel cell stackis not limited to excessiveness or scarceness of water contained in afuel cell stack, and a phenomenon caused by such an abnormality is notlimited to abnormal voltage behavior in the cell or the cell block inthe fuel cell stack. Therefore, since the operational state isdetermined based on the voltage behavior, an erroneous determination maybe made. Particularly, when other abnormalities of the fuel cell stackare to be determined in addition to the aforementioned abnormalities, anappropriate determination cannot be made.

SUMMARY OF THE INVENTION

[0007] An object of a diagnostic apparatus and a diagnostic method for afuel cell according to the invention is to more accurately determine astate of the fuel cell. It is another object of the diagnostic apparatusand the diagnostic method for a fuel cell according to the invention tomore accurately determine plural abnormalities that may occur in thefuel cell. It is a further object of the diagnostic apparatus for a fuelcell according to the invention to diagnose the state of the fuel cellwhile the fuel cell is held in operation without operating a fuel gassupply system or a cooling system installed in a moving object.

[0008] In order to achieve at least part of the aforementioned objects,the diagnostic apparatus and the diagnostic method for a fuel cellaccording to the invention are provided as follows.

[0009] According to an aspect of the invention, a diagnostic apparatuswhich diagnoses a state of the fuel cell includes an operation devicewhich is used for operating the fuel cell; an operational statedetecting portion which detects a change in an operational state of thefuel cell; a device control portion which controls the operation devicesuch that the fuel cell is operated according to at least onepredetermined operation pattern; and a diagnostic portion whichdiagnoses the state of the fuel cell based on the change in theoperational state of the fuel cell that is detected by the operationalstate detecting portion when the fuel cell is operated by the devicecontrol portion according to the at least one predetermined operationpattern, and the at least one predetermined operation pattern.

[0010] In the diagnostic apparatus according to the aforementionedaspect, the fuel cell is operated according to the at least onepredetermined operation pattern, and the state of the fuel cell isdiagnosed based on the change in the operational state of the fuel cellthat is detected when the fuel cell is operated, and the at least onepredetermined operation pattern. Therefore, it is possible to diagnosethe state of the fuel cell accurately, as compared with a case where thestate of the fuel cell is diagnosed based on only voltage behavior.

[0011] In the diagnostic apparatus according to the aforementionedaspect, the diagnostic portion may diagnose the state of the fuel cellby comparing the change in the operational state of the fuel cellcorresponding to each of the operation patterns, which is detected bythe operational state detecting portion when the fuel cell is operatedby the device control portion according to the at least onepredetermined operation pattern, with a change in a normal operationalstate of the fuel cell corresponding to each of the operation patterns,which is detected by the operational state detecting portion when thefuel cell that normally functions is operated by the device controlportion according to the at least one predetermined operation pattern.Also, a relationship between the state of the fuel cell, and presence orabsence of an abnormality in the change in the operational state of thefuel cell corresponding to each of the operation patterns may be set inthe diagnostic portion in advance.

[0012] In the diagnostic apparatus according to the aforementionedaspect, the operational state detecting portion may detect, as theoperational state of the fuel cell, an output current and an outputvoltage of the fuel cell, and the diagnostic portion may diagnose thestate of the fuel cell based on the detected output current and thedetected output voltage. Thus, it is possible to more accuratelydiagnose an abnormality which causes characteristic behavior of theoutput current and the output voltage, among abnormalities that mayoccur in the fuel cell.

[0013] In the diagnostic apparatus according to the aforementionedaspect, the operational state detecting portion may detect, as theoperational state of the fuel cell, an interterminal voltage and/or acell voltage when the fuel cell is in an open state, and the diagnosticportion may diagnose the state of the fuel cell based on the detectedinterterminal voltage and/or the detected cell voltage. Thus, it ispossible to more accurately diagnose an abnormality which causescharacteristic behavior of the interterminal voltage and/or the cellvoltage when the fuel cell is in the open state, among abnormalitiesthat may occur in the fuel cell. The “cell voltage” includes a voltagein a cell, and a voltage in a cell block including plural cells.

[0014] In the diagnostic apparatus according to the aforementionedaspect, the operation device may be a gas supply device which is usedfor supplying a fuel gas and/or an oxidative gas to the fuel cell, andthe device control portion may control, according to one of the at leastone predetermined operation pattern, the gas supply device such that thefuel gas and/or the oxidative gas is supplied to the fuel cell accordingto a predetermined supply pattern. Also, in the diagnostic apparatus,the predetermined supply pattern may include one of a predeterminedpattern of increasing/decreasing a flow amount of the fuel gas and/orthe oxidative gas, a predetermined pattern of increasing/decreasing asupply pressure, and a predetermined pattern of increasing/decreasing adegree of humidification. Thus, it is possible to more accuratelydiagnose the state of the fuel cell, which is caused by anincrease/decrease in the flow amount of the fuel gas and/or theoxidative gas, an increase/decrease in the supply pressure, or anincrease/decrease in the degree of humidification.

[0015] In the diagnostic apparatus according to the aforementionedaspect, the operational state detecting portion may detect, as theoperational state of the fuel cell, an internal resistance of the fuelcell, and the diagnostic portion may diagnose the state of the fuel cellbased on the detected internal resistance. Thus, it is possible to moreaccurately diagnose an abnormality which causes characteristic behaviorof the internal resistance of the fuel cell, among abnormalities whichmay occur in the fuel cell.

[0016] In the diagnostic apparatus according to the aforementionedaspect, the operation device may be a temperature adjusting device whichis used for adjusting an operation temperature of the fuel cell, and thedevice control portion may control, according to one of the at least onepredetermined operation pattern, the temperature adjusting device suchthat the fuel cell is operated according to a predetermined temperaturepattern. Thus, it is possible to more accurately diagnose the state ofthe fuel cell, which is caused by a change in the operation temperatureof the fuel cell.

[0017] In the diagnostic apparatus according to the aforementionedaspect, the operational state detecting portion may detect, as theoperational state of the fuel cell, one of a temperature of the fuelcell, an exhaust gas temperature in a fuel gas system, and an exhaustgas temperature in an oxidative gas system, and the diagnostic portionmay diagnose the state of the fuel cell based on one of the temperatureof the fuel cell, the exhaust gas temperature in the fuel gas system,and the exhaust gas temperature in the oxidative gas system, which isdetected. Thus, it is possible to more accurately diagnose anabnormality which causes characteristic behavior of one of thetemperature of the fuel cell, the exhaust gas temperature in the fuelgas system, and the exhaust gas temperature in the oxidative gas system.

[0018] In the diagnostic apparatus according to the aforementionedaspect, the diagnostic portion may determine that there is a mechanicalfailure or deterioration due to a secular change when an output voltageof the fuel cell is less than a predetermined value in a case where thefuel cell is operated according to the at least one predeterminedoperation pattern. Thus, it is possible to make a diagnosis of amechanical failure or deterioration due to a secular change.

[0019] In a diagnostic apparatus for a fuel cell according to anotheraspect of the invention, which is used for diagnosing a state of a fuelcell installed in a moving object as a power source, the operationdevice may include a device installed in the moving object, theoperational state detecting portion may include a moving objectdetecting portion which is installed in the moving object, and whichdetects a state as the operational state of the fuel cell, the devicecontrol portion may be able to be connected to a control system which isinstalled in the moving object for controlling an operation of the fuelcell, and may control the operation device by giving an instruction tothe control system, and the operation device may include a poweradjusting portion which adjusts power generated by the fuel cell. Thus,it is possible to diagnose the fuel cell installed in the moving objectwhile the moving object is stopped. In the diagnostic apparatus for afuel cell according to the aforementioned aspect of the invention, thepower adjusting portion may be connected to an output terminal of thefuel cell, and may adjust the power generated by the fuel cell byabsorbing or consuming the power.

[0020] The diagnostic apparatus for a fuel cell according to theaforementioned aspect, which is used for diagnosing the fuel cellinstalled in the moving object, may further include a fuel gas supplyportion which supplies the fuel cell with a fuel gas that is used forpower generation of the fuel cell, instead of a fuel gas supply systemwhich is installed in the moving object for supplying the fuel cell withthe fuel gas, or may further include a cooling portion which cools thefuel cell, instead of a cooling system which is installed in the movingobject for cooling the fuel cell. Thus, even when an abnormality occursin the fuel gas supply system or the cooling system which is installedin the moving object, it is possible to diagnose the fuel cell installedin the moving object.

[0021] According to a further aspect of the invention, a diagnosticmethod for a fuel cell, which is a method for diagnosing a state of thefuel cell, includes the steps of: (a) operating the fuel cell accordingto at least one predetermined operation pattern; (b) detecting a changein an operational state of the fuel cell corresponding to each of theoperation patterns when the fuel cell is operated according to the atleast one predetermined operation pattern; and (c) diagnosing the stateof the fuel cell based on the detected change in the operational stateand the at least one predetermined operation pattern.

[0022] In the diagnostic method according to the aforementioned aspect,the change in the operational state of the fuel cell when the fuel cellis operated according to the at least one predetermined operationpattern is detected, and the state of the fuel cell is diagnosed basedon the change in the operational state of the fuel cell that is detectedwhen the fuel cell is operated according to the at least onepredetermined operation pattern, and the at least one predeterminedoperation pattern. Therefore, it is possible to more accurately diagnosethe state of the fuel cell, as compared with a case where the state ofthe fuel cell is diagnosed based on only voltage behavior.

[0023] In the diagnostic method according to the aforementioned aspect,in the step (c), the state of the fuel cell may be diagnosed bycomparing the change in the operational state of the fuel cellcorresponding to each of the operation patterns, which is detected whenthe fuel cell is operated according to the at least one predeterminedoperation pattern, with a change in a normal operational state of thefuel cell corresponding to each of the operation patterns, which isdetected when the fuel cell that normally functions is operatedaccording to the at least one predetermined operation pattern.

[0024] In the diagnostic method according to the aforementioned aspect,in the step (a), the fuel cell may be operated according to one of apredetermined pattern of increasing/decreasing a flow amount of a fuelgas and/or an oxidative gas that is supplied to the fuel cell, apredetermined pattern of increasing/decreasing a supply pressure, and apredetermined pattern of increasing/decreasing a degree ofhumidification, as one of the operation patterns. Thus, it is possibleto more accurately diagnose the state of the fuel cell, which is causedby an increase/decrease in the flow amount of the fuel gas and/or theoxidative gas, an increase/decrease in the supply pressure, or anincrease/decrease in the degree of humidification.

[0025] In the diagnostic method according to the aforementioned aspect,in the step (b), one of i) an output current and an output voltage ofthe fuel cell, ii) an interterminal voltage or a cell voltage when thefuel cell is in an open state, iii) an internal resistance of the fuelcell, iv) a temperature of the fuel cell, v) an exhaust gas temperaturein a fuel gas system of the fuel cell, and vi) an exhaust gastemperature in an oxidative gas system of the fuel cell may be detectedas the operational state. Thus, it is possible to more accuratelydiagnose an abnormality which causes characteristic behavior of one ofi) the output current and the output voltage of the fuel cell, ii) theinterterminal voltage of the cell voltage when the fuel cell is in theopen state, iii) the internal resistance of the fuel cell, iv) thetemperature of the fuel cell, v) the exhaust gas temperature in the fuelgas system, and vi) the exhaust gas temperature in the oxidative gassystem.

BRIEF DESCRIPTION OF THE DRAWINGS

[0026]FIG. 1 is a conceptual view exemplifying a constructional conceptin diagnosing a state of a fuel cell 122 installed in a vehicle 110 bymeans of a fuel-cell diagnostic apparatus 20 in accordance with oneembodiment of the invention;

[0027]FIG. 2 is a block diagram showing the overall construction of afuel cell system 120 installed in the vehicle;

[0028]FIG. 3 is a block diagram showing the overall construction of thediagnostic apparatus 20 of the embodiment;

[0029]FIG. 4 is a flowchart showing an example of a diagnostic processperformed by the fuel-cell diagnostic apparatus 20 according to theembodiment of the invention;

[0030]FIGS. 5A and 5B are tables, each describing an example ofcombinations of states of the fuel cell and check results; and

[0031]FIG. 6 is an explanatory view showing a drive unit 45 as anexample.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0032] Next, a mode of implementing the invention will be describedbased on the embodiment thereof. FIG. 1 is a conceptual viewexemplifying a constructional concept in diagnosing a state of the fuelcell 122 installed in the vehicle 110 by means of the fuel-celldiagnostic apparatus 20 in accordance with one embodiment of theinvention. FIG. 2 is a block diagram showing the overall construction ofthe fuel cell system 120 installed in the vehicle. FIG. 3 is a blockdiagram showing the overall construction of the diagnostic apparatus 20of the embodiment. For convenience of explanation, the construction ofthe fuel cell system 120 installed in the vehicle 110 will be describedfirst, and then the construction of the fuel-cell diagnostic apparatus20 of the embodiment will be described in detail.

[0033] As shown in FIG. 2, the fuel cell system 120 includes a fuel gassupply system 130 that supplies a fuel cell 122 with hydrogen and air asfuel, a power adjustment system 140 that adjusts power generated by thefuel cell 122 with a view to using the power to drive a vehicle oraccumulating the power, a cooling system 150 that cools the fuel cell122, and a vehicle-operation control unit 160 that controls operation ofthe fuel cell 122 while controlling a running state of the vehicle.

[0034] For example, the fuel cell 122 is constructed as aproton-exchange membrane fuel cell made of a plurality of laminatedcells, each of which includes a polymer membrane exhibiting good protonconductivity in a wet state as an electrolytic membrane. Power isgenerated through an electrochemical reaction that is caused bysupplying hydrogen and oxygen respectively to a fuel-electrode-side flowpassage and an air-electrode-side flow passage that are formed onopposed sides of the electrolytic membrane.

[0035] The fuel gas supply system 130 includes a hydrogen tank 131 thatstores high-pressure hydrogen and that is connected to thefuel-electrode-side flow passage of the fuel cell 122 via an adjustingvalve 132, a hydrogen pump 133 that causes hydrogen supplied from thehydrogen tank 131 to circulate through a circulation passage includingthe fuel-electrode-side flow passage of the fuel cell 122, an air supplypump 134 that supplies the air-electrode-side flow passage of the fuelcell 122 with air as an oxidative gas containing oxygen, and humidifiers135, 136 which humidify hydrogen and air supplied to the fuel cell 122.A fuel gas supply unit fitting portion 139 for fitting a fuel gas supplyunit 30 of the fuel-cell diagnostic apparatus 20 of the embodiment isprovided in the fuel gas supply system 130 at a position to be connectedto the fuel cell 122.

[0036] The power adjustment system 140 includes a battery 142 connectedto an output terminal of the fuel cell 122 via a DC/DC converter 141,and a traction motor 144 connected to the output terminal of the fuelcell 122 via an inverter 143. The power adjustment system 140 isdesigned such that the traction motor 144 can consume power and that thebattery 142 can be charged with electricity and electricity can bedischarged from the battery 142. A power adjustment unit fitting portion149 for fitting a power adjustment unit 40 of the fuel-cell diagnosticapparatus 20 of the embodiment is provided in the power adjustmentsystem 140 at a position to be connected to the fuel cell 122.

[0037] The cooling system 150 is constructed as a circulation passageincluding a flow passage of coolant for the fuel cell 122. The coolingsystem 150 includes a radiator 151 that air-cools coolant, and a coolantpump 152 that causes coolant to circulate. By causing coolant cooled bythe radiator 151 to circulate through the circulation passage, thecooling system 150 cools the fuel cell 122. A cooling unit fittingportion 159 for fitting a cooling unit 50 of the fuel-cell diagnosticapparatus 20 of the embodiment is provided in the cooling system 150 ata position to be connected to the fuel cell 122.

[0038] The vehicle-operation control unit 160 is constructed as amicrocomputer mainly composed of a CPU (not shown), and includes aninput port, an output port, and a communication port. Thevehicle-operation control unit 160 receives, via the input port, signalsindicating a cell voltage detected by a voltage sensor for detecting avoltage between cells constituting the fuel cell 122, a fuel celltemperature T detected by a temperature sensor 122 a attached to thefuel cell 122, an interterminal voltage V detected by a voltage sensor123 attached to a power line in the vicinity of an output terminal ofthe fuel cell 122, an output current I detected by a current sensor 124attached to the power line in the vicinity of the output terminal of thefuel cell 122, a voltage detected by a voltage sensor (not shown)attached to the DC/DC converter 141, a current detected by a currentsensor (not shown) attached to the DC/DC converter 141, acharge/discharge voltage detected by a voltage sensor (not shown)attached to a power line in the vicinity of an output terminal of thebattery 142, a charge/discharge current detected by a current sensor(not shown) attached to the power line in the vicinity of the outputterminal of the battery 142, a phase current of the traction motor 144detected by a current sensor (not shown) attached to a power lineextending from an inverter 143 to the traction motor 144, a position ofa rotor detected by a rotational position sensor (not shown) attached tothe traction motor 144, and the like. The vehicle-operation control unit160 outputs, via the output port, a drive signal for the adjusting valve132, a drive signal for the hydrogen pump 133, a drive signal for theair supply pump 134, a drive signal for the humidifiers 135, 136, aswitching control signal for the DC/DC converter 141, a switchingcontrol signal for the inverter 143, a drive signal for the coolant pump152, and the like. A connector 169 for connection to a control unit 60of the fuel-cell diagnostic apparatus 20 of the embodiment is connectedto the communication port of the vehicle-operation control unit 160.

[0039] Next, the construction of the fuel-cell diagnostic apparatus 20of the embodiment will be described. As shown in FIGS. 1 and 3, thefuel-cell diagnostic apparatus 20 of the embodiment includes the fuelgas supply unit 30 that supplies the fuel cell 122 with hydrogen and airas fuel, the power adjustment unit 40 that adjusts power generated bythe fuel cell 122, and the cooling unit 50 that cools the fuel cell 122,instead of the fuel gas supply system 130 of the fuel cell system 120,the power adjustment system 140 of the fuel cell system 120, and thecooling system 150 of the fuel cell system 120, respectively. Thefuel-cell diagnostic apparatus 20 also includes the control unit 60 thatis connected to the vehicle-operation control unit 160 of the fuel cellsystem 120 so as to exchange communications therewith and that controlsthe entire apparatus.

[0040] As shown in FIG. 3, the fuel gas supply unit 30 includes ahydrogen tank 31 whose outlet and inlet are provided with adjustingvalves 32, a hydrogen pump 33 for causing hydrogen to circulate, an airsupply pump 34 for supplying air, and humidifiers 35, 36 for humidifyinghydrogen and air that are supplied. When fitted to the fuel gas supplyunit fitting portion 139 of the fuel cell system 120 by means of a fuelgas supply system fitting portion 39, the fuel gas supply unit 30functions substantially in the same manner as the fuel gas supply system130 of the fuel cell system 120.

[0041] The power adjustment unit 40 includes a DC/DC converter 41capable of raising and lowering a direct-current voltage, and achargeable/dischargeable battery 42 that is connected to the DC/DCconverter 41. When connected to the power adjustment unit fittingportion 149 of the fuel cell system 120 by means of a power adjustmentsystem fitting portion 49, the power adjustment unit 40 can freelycharge the battery 42 with power generated by the fuel cell 122. Avoltage sensor 43 for detecting a voltage applied to the fuel cell 122and a current sensor 44 for detecting a current flowing through the fuelcell 122 are attached to the DC/DC converter 41 on the side of the poweradjustment system fitting portion 49.

[0042] The cooling unit 50 includes a radiator 51 that cools coolant bymeans of outside air, and a coolant pump 52 for causing coolant tocirculate. When fitted to the cooling unit fitting portion 159 by meansof a cooling system fitting portion 59, the cooling unit 50 functionssubstantially in the same manner as the cooling system 150 of the fuelcell system 120.

[0043] As shown in FIG. 1, the control unit 60 is functionally composedof an operation control portion 61 that controls operation of the fuelcell 122 by means of the vehicle-operation control unit 160, adiagnostic portion 62 that diagnoses a state of the fuel cell 122 on thebasis of a state of the fuel cell 122 that is in operation, and a unitcontrol portion 63 that controls the fuel gas supply unit 30, the poweradjustment unit 40, and the cooling unit 50. As shown in FIG. 3, thecontrol unit 60 is hardwarewise constructed as a microcomputer mainlycomposed of a CPU 65, a ROM 66, and a RAM 67. The control unit 60receives, via an input port (not shown), signals indicating a voltagedetected by the voltage sensor 43, a current detected by the currentsensor 44, and the like. The control unit 60 outputs, via an output port(not shown), a drive signal for the adjusting valve 32, a drive signalfor the hydrogen pump 33, a drive signal for the air supply pump 34, aswitching control signal for the DC/DC converter 41, a drive signal forthe coolant pump 52, and the like. A connector 69 that can be connectedto the connector 169 connected to the communication port of thevehicle-operation control unit 160 of the fuel cell system 120 isattached to a communication port (not shown) of the control unit 60.

[0044] Next, it will be described how a diagnosis of a state of the fuelcell 122 installed in the vehicle 110 is made using the fuel-celldiagnostic apparatus 20 of the embodiment constructed as describedabove. First to fourth diagnostic patterns are set for the fuel-celldiagnostic apparatus 20 of the embodiment. According to the firstdiagnostic pattern, a diagnosis is made with the control unit 60 and thevehicle-operation control unit 160 being connected via the connector 69and the connector 169 and with the power adjustment system fittingportion 49 being fitted to the power adjustment unit fitting portion 149so that the power adjustment unit 40 is connected to the fuel cellsystem 120. According to the second diagnostic pattern, a diagnosis ismade with the fuel gas supply system fitting portion 39 being fitted tothe fuel gas supply unit fitting portion 139 so that the fuel gas supplyunit 30 is connected to the fuel cell system 120, in addition to theconfiguration of the first diagnostic pattern. According to the thirddiagnostic pattern, a diagnosis is made with the cooling system fittingportion 59 being fitted to the cooling unit fitting portion 159 so thatthe cooling unit 50 is connected to the fuel cell system 120, inaddition to the configuration of the first diagnostic pattern. Accordingto the fourth diagnostic pattern, a diagnosis is made with the fuel gassupply unit 30, the power adjustment unit 40, and the cooling unit 50being all connected to the fuel cell system 120. That is, the firstdiagnostic pattern is used when the fuel gas supply system 130 and thecooling system 150 as well as a state of the fuel cell 122 are diagnosedwhile the fuel gas supply system 130 and the cooling system 150 are heldin operation. The second diagnostic pattern is used when there is anabnormality occurring in the fuel gas supply system 130 or when adiagnosis is made without taking the influence of the fuel gas supplysystem 130 into account. The third diagnostic pattern is used when thereis an abnormality occurring in the cooling system 150 or when adiagnosis is made without taking the influence of the cooling system 150into account. The fourth diagnostic pattern is used when there areabnormalities occurring in the fuel gas supply system 130 and thecooling system 150 or when a diagnosis is made only as to the fuel cell122 without taking the influences of the fuel gas supply system 130 andthe cooling system 150 into account. Only the connection relationshipbetween the fuel gas supply unit 30 or the cooling unit 50 and the fuelcell system 120 is different among the diagnostic patterns, and the samediagnostic process is performed in all the diagnostic patterns.Therefore, hereinafter, the fourth diagnostic pattern will be described.

[0045]FIG. 4 is a flowchart showing an example of a diagnostic processperformed by the control unit 60 in the fuel-cell diagnostic apparatus20 according to the embodiment of the invention. In the diagnosticprocess according to the embodiment, plural checks are performed basedon behavior of the fuel cell 122 caused by a change in the operationalstate (step S100 to S160), and then an overall diagnosis of the state ofthe fuel cell 122 is performed based on results of the checks (stepS170). The check items include a check on deterioration of acurrent/voltage characteristic (hereinafter, referred to as a IVcharacteristic) of the fuel cell 122 (step S100), a check on anexcessive decrease in the interterminal voltage or the cell voltagebetween the plural cells constituting the fuel cell 122 when the outputterminals of the fuel cell 122 are in the open state (step S110), acheck on excessive influence of a change in the supply amount or thepressure of hydrogen on a generated current I and a generated voltage V(step S120), a check on excessive influence of a change in the supplyamount or the pressure of air on the generated current I and generatedvoltage V (step S130), a check on an excessive internal resistance (stepS140), a check on excessive influence of a change in the operationtemperature of the fuel cell 122 on the generated current I andgenerated voltage V (step S150), a check on excessive influence of achange in a humidification amount for hydrogen and air on the generatedcurrent I and the generated voltage V (step S160), and the like. In theembodiment, the flowchart in FIG. 4 shows the order in which the checksare performed. However, the order is not essential, and may be changed.Hereinafter, each of the check items will be described.

[0046] Specifically, the check on deterioration of the IV characteristic(step S100) is performed as follows. After the fuel gas supply unit 30,the power adjustment unit 40, and the cooling unit 50 are operated suchthat the fuel cell 122 fully performs the function in a steady state,the generated current I of the fuel cell 122 is changed using control bythe DC/DC converter 41 in the power adjustment unit 40, and thegenerated voltage V which is changed due to a change in the generatedcurrent I is detected. Then, it is determined whether or not a deviationbetween a relationship between the generated current I and the generatedvoltage V (characteristic) and the IV characteristic of the fuel cellwhich normally functions is in an allowable range. In this case, as thegenerated current I and the generated voltage V, the values detected bythe current sensor 44 and the voltage sensor 43 in the power adjustmentunit 40 may be used, or the values detected by the current sensor 124and the voltage sensor 123 may be used.

[0047] Specifically, the check on an excessive decrease in theinterterminal voltage or the cell voltage when the output terminals ofthe fuel cell 122 are in the open state (step S110) is performed asfollows. While the fuel gas supply unit 30 supplies sufficient hydrogenand air to the fuel cell 122, the generated current I is decreased tovalue 0 by the power adjustment unit 40. In this state, the voltagedetected by the voltage sensor 43 or the voltage sensor 143 (theinterterminal voltage of the fuel cell 122) and the cell voltagedetected by the voltage sensor (not shown) for detecting the voltagebetween the cells constituting the fuel cell 122 are compared with theinterterminal voltage and the cell voltage which are detected when thefuel cell that normally functions is in the same state. Thus, it isdetermined whether or not a decrease in the interterminal voltage or thecell voltage is in an allowable range. The cell voltage may be thevoltage in each cell or may be the voltage in a cell block includingplural cells.

[0048] Specifically, the check on excessive influence of a change in thesupply amount or the pressure of hydrogen on the generated current I andthe generated voltage V (step S120) is performed as follows. After thefuel cell 122 is brought into the steady operational state, the openingof the adjusting valve 32 of the fuel gas supply unit 30 is changed, andthe generated current I and the generated voltage V when the amount andthe pressure of hydrogen supplied to the fuel cell 122 are changed aredetected. Then, a degree of a change in a relationship between thegenerated current I and the generated voltage V is compared with adegree of a change in a relationship between the generated current I andthe generated voltage V when the fuel cell that normally functions isoperated in the same manner. Thus, it is determined whether or not adeviation between both the degrees is in an allowable range. In thiscase, when the check is performed by changing only the supply amount ofhydrogen without changing the pressure of hydrogen, or by changing onlythe pressure of hydrogen without changing the supply amount of hydrogen,influence of the change in the supply amount of hydrogen or influence ofthe change in the supplied pressure can be checked.

[0049] The check on excessive influence of a change in the supply amountor the pressure of air on the generated current I and the generatedvoltage V (step S130) is performed in the same manner as theaforementioned check on excessive influence of a change in the supplyamount or the pressure of hydrogen. The step S120 and step S130 can beperformed separately, or the step S120 and step S130 can be combined soas to be performed simultaneously. When the step S120 and step S130 arecombined and performed simultaneously, a change in the supply amount ofhydrogen, a change in the pressure of hydrogen, a change in the supplyamount of air, and a change in the pressure of air can be combined invarious manners. Thus, the check can be performed by various methods,for example, by increasing or decreasing the supply amount of hydrogenand the supply amount of air while maintaining a mole ratio betweenhydrogen and oxygen in electrochemical reaction in the fuel cell 122, byincreasing or decreasing one of the supply amount of hydrogen and thesupply amount of air without changing the other supply amount, or byincreasing/decreasing the deviation between the pressure of hydrogen andthe pressure of air.

[0050] Specifically, the check on excessive internal resistance (stepS140) is performed as follows. The internal resistance is calculatedbased on the generated current I and the generated voltage V of the fuelcell 122. Then, it is determined whether or not a value by which theinternal resistance is higher than the internal resistance that isestimated considering elapsed time since start of use is in an allowablerange.

[0051] Specifically, the check on excessive influence of a change in theoperation temperature of the fuel cell 122 on the generated current Iand generated voltage V (step S150) is performed as follows. Thetemperature of the fuel cell 122 is changed by performing drive controlof the coolant pump 52 in the cooling unit 50 based on the fuel celltemperature detected by the temperature sensor (not shown) fitted to thefuel cell 122, and the generated current I and the generated voltage Vare detected while the temperature of the fuel cell 122 is changed. Adegree of a change in a relationship between the generated current I andthe generated voltage V is compared with a degree of a change in arelationship between the generated current I and the generated voltage Vwhich are detected when the fuel cell that normally functions is in thesame state. Thus, it is determined whether or not a deviation betweenboth the degrees is in an allowable range. The temperature of the fuelcell 122 can be obtained by inputting the signal sent from thetemperature sensor (not shown) fitted to the fuel cell 122 to thecontrol unit 60 via the vehicle-operation control unit 160.

[0052] The check on excessive influence of a change in thehumidification amount for hydrogen and air on the generated current Iand the generated voltage V (step S160) is performed as follows. Thehumidification amount for hydrogen and air that are supplied to the fuelcell 122 is changed, and the generated current I and the generatedvoltage V are detected while the humidification amount is changed. Adegree of a change in a relationship between the generated current I andthe generated voltage V is compared with a degree of a change in arelationship between the generated current I and the generated voltage Vwhich are detected when the fuel cell that normally functions is in thesame state. Thus, it is determined whether or not a deviation betweenboth the degrees is in an allowable range.

[0053] In the embodiment, a diagnosis is made in step S170 as follows.The aforementioned checks are performed while the fuel cell is invarious states including abnormalities and the like. Results of thechecks are stored as database in advance. The diagnosis is made byderiving a state which corresponds to the results of the checksperformed on the fuel cell 122 under the diagnosis. FIGS. 5A and 5B aretables, each describing an example of combinations of states of the fuelcell and check results. In FIGS. 5A and 5B, a circle signifies that itis determined that deterioration or excessive influence exists. A mark xsignifies that it is determined that deterioration or excessiveinfluence does not exist. A triangle signifies that deterioration orexcessive influence may or may not exist. A question mark signifies thata determination is difficult to make. In the case where the diagnosis ismade, the triangle and the question mark may be regarded as either thecircle or the mark x. In the embodiment, when a predetermined outputvoltage is not obtained even after the fuel cell is operated accordingto all operation patterns for check in the case where the diagnosis ismade, it is determined that there is a mechanical failure other than “acontact failure of a cell monitor terminal” and “an abnormality of acell monitor substrate”, or deterioration occurs since the fuel cell isused for a long time. The combinations of the states of the fuel celland the check results shown in FIGS. 5A and 5B are exemplary, and thecombinations thereof vary depending on the type, characteristics, andthe like of the fuel cell.

[0054] In the fuel-cell diagnostic apparatus 20 of the embodimentdescribed hitherto, the detected values such as the generated current Iand the generated voltage V which are detected when the fuel cell 122 isoperated according to the operation pattern corresponding to each checkitem, that is, the operation pattern for check with the detected valueswhich are obtained when the fuel cell that normally functions issimilarly operated according to the operation pattern for check, wherebythe diagnosis of the state of the fuel cell 122 can be made.Particularly, since the plural checks are performed, and the results ofthe plural checks are used to make the diagnosis of the state of thefuel cell 122, the diagnosis of the state of the fuel cell 122 can bemade more accurately. Further, when the predetermined output voltage isnot obtained even after the fuel cell 122 is operated according to theoperation pattern for check, it can be determined that there is amechanical failure or deterioration occurs since the fuel cell is usedfor a long period.

[0055] The fuel-cell diagnostic apparatus 20 of the embodiment describedhitherto can diagnose the state of the fuel cell 122 while the fuel cell122 is held in operation during stoppage of the vehicle 110, withoutremoving the fuel cell 122 installed in the vehicle 110 therefrom.Moreover, even if there is an abnormality occurring in the fuel gassupply system 130 or the cooling system 150 of the fuel cell system 120,the fuel-cell diagnostic apparatus 20 can diagnose the state of the fuelcell 122 while the fuel cell 122 is held in operation with the fuel gassupply unit 30 or the cooling unit 50 being connected thereto.

[0056] In the fuel-cell diagnostic apparatus 20 of the embodiment, allthe checks in step S100 to step S160 are performed, and then thediagnosis of the state of the fuel cell 122 is made. However, all thechecks are not necessarily performed, and only part of the checks may beperformed. Obviously, a check other than the checks in the embodimentmay be performed. Various examples of the check other than those in theembodiment include a check on excessive influence of a change in anexhaust gas temperature in a hydrogen system or an exhaust gastemperature in an air system on the generated current I and thegenerated voltage V, excessive influence of a change in a back pressurein the hydrogen system or a back pressure in the air system on thegenerated current I and the generated voltage V, and excessive influenceof vibration of the vehicle 110 on the generated current I and thegenerated voltage V.

[0057] In the fuel-cell diagnostic apparatus 20 of the embodiment, theDC/DC converter 41 and the battery 42 are employed as the poweradjustment unit 40. However, as long as power generated by the fuel cell122 can be adjusted, a power-consuming load can be employed instead ofthe battery 42.

[0058] In the fuel-cell diagnostic apparatus 20 of the embodiment, powergenerated by the fuel cell 122 is adjusted by the power adjustment unit40. However, it is also appropriate that power generated by the fuelcell 122 be adjusted using the DC/DC converter 141 and the battery 142of the power adjustment system 140 of the fuel cell system 120. In thiscase, it is appropriate that power generated by the fuel cell 122 beadjusted by outputting a switching control signal to the DC/DC converter141 via the vehicle-operation control unit 160. It is also appropriatethat power generated by the fuel cell 122 be consumed by the tractionmotor 144 of the power adjustment system 140 of the fuel cell system120. In this case, as exemplified in FIG. 4, it is appropriate to employthe drive unit 45 or the like, which is capable of applyingsubstantially the same load as in a running state of the vehicle 110 todriving wheels 114 thereof by means of load-applying rollers 46 a and 46b. Thus, the fuel cell 122 can be diagnosed with the fuel cell system120 installed in the vehicle 110 assuming substantially the same stateas the state while the vehicle 110 is running.

[0059] The fuel-cell diagnostic apparatus 20 of the embodiment isdesigned to diagnose the state of the fuel cell 122 of the fuel cellsystem 120 installed in the vehicle 110. However, the fuel-celldiagnostic apparatus 20 may also be designed to diagnose a state of afuel cell of a fuel cell system installed in a moving object other thanthe vehicle 110, such as an airplane and a ship. Alternatively, thefuel-cell diagnostic apparatus 20 may also be designed to diagnose astate of fuel cell which is not installed in a moving object.

[0060] In the fuel-cell diagnostic apparatus 20 of the embodimentincludes the fuel gas supply unit 30, the power adjustment unit 40, thecooling unit 50, and the control unit 60, separately from the fuel cellsystem 120. However, the fuel gas supply system 130, the poweradjustment system 140, the cooling system 150, or the vehicle-operationcontrol unit 160 of the fuel cell system 120 may function as eachportion of the fuel-cell diagnostic apparatus 20 according to theembodiment. In other words, the fuel cell system 120 may have functionsof the fuel-cell diagnostic apparatus 20 according to the embodiment.

[0061] In the embodiment, the fuel-cell diagnostic apparatus 20 has beendescribed, which diagnoses the state of the fuel cell based on a changein the operational state of the fuel cell that is detected when the fuelcell is operated according to the predetermined operations patterns.Obviously, however, the invention can be applied to a diagnostic methodfor a fuel cell.

[0062] Although the embodiment of the invention has been described, itis to be understood that the invention is not limited to the embodiment,and the invention can be realized in various embodiments withoutdeparting from the true spirit of the invention

What is claimed is:
 1. A diagnostic apparatus for a fuel cell, whichdiagnoses a state of the fuel cell, comprising: an operation devicewhich is used for operating the fuel cell; an operational statedetecting portion which detects a change in an operational state of thefuel cell; a device control portion which controls the operation devicesuch that the fuel cell is operated according to at least onepredetermined operation pattern; and a diagnostic portion whichdiagnoses the state of the fuel cell based on the change in theoperational state of the fuel cell that is detected by the operationalstate detecting portion when the fuel cell is operated by the devicecontrol portion according to the at least one predetermined operationpattern, and the at least one predetermined operation pattern.
 2. Thediagnostic apparatus for a fuel cell according to claim 1, wherein thediagnostic portion diagnoses the state of the fuel cell by comparing thechange in the operational state of the fuel cell corresponding to eachof the operation patterns, which is detected by the operational statedetecting portion when the fuel cell is operated by the device controlportion according to the at least one predetermined operation pattern,with a change in a change in a normal operational state of the fuel cellcorresponding to each of the operation patterns, which is detected bythe operational state detecting portion when the fuel cell that normallyfunctions is operated by the device control portion according to the atleast one predetermined operation pattern.
 3. The diagnostic apparatusfor a fuel cell according to claim 2, wherein a relationship between thestate of the fuel cell, and presence or absence of an abnormality in thechange in the operational state of the fuel cell corresponding to eachof the operation patterns is set in the diagnostic portion in advance.4. The diagnostic apparatus for a fuel cell according to claim 1,wherein the operational state detecting portion detects, as theoperational state of the fuel cell, an output current and an outputvoltage of the fuel cell, and the diagnostic portion diagnoses the stateof the fuel cell based on the detected output current and the detectedoutput voltage.
 5. The diagnostic apparatus for a fuel cell according toclaim 1, wherein the operational state detecting portion detects, as theoperational state of the fuel cell, an interterminal voltage and/or acell voltage when the fuel cell is in an open state, and the diagnosticportion diagnoses the state of the fuel cell based on the detectedinterterminal voltage and/or the detected cell voltage.
 6. Thediagnostic apparatus for a fuel cell according to claim 1, wherein theoperation device is a gas supply device which is used for supplying afuel gas and/or an oxidative gas to the fuel cell, and the devicecontrol portion controls, according to one of the at least onepredetermined operation pattern, the gas supply device such that thefuel gas and/or the oxidative gas is supplied to the fuel cell accordingto a predetermined supply pattern.
 7. The diagnostic apparatus for afuel cell according to claim 6, wherein the predetermined supply patternincludes one of a predetermined pattern of increasing/decreasing a flowamount of the fuel gas and/or the oxidative gas, a predetermined patternof increasing/decreasing a supply pressure, and a predetermined patternof increasing/decreasing a degree of humidification.
 8. The diagnosticapparatus for a fuel cell according to claim 1, wherein the operationalstate detecting portion detects, as the operational state of the fuelcell, an internal resistance of the fuel cell, and the diagnosticportion diagnoses the state of the fuel cell based on the detectedinternal resistance.
 9. The diagnostic apparatus for a fuel cellaccording to claim 1, wherein the operation device is a temperatureadjusting device which is used for adjusting an operation temperature ofthe fuel cell, and the device control portion controls, according to oneof the at least one predetermined operation pattern, the temperatureadjusting device such that the fuel cell is operated according to apredetermined temperature pattern.
 10. The diagnostic apparatus for afuel cell according to claim 1, wherein the operational state detectingportion detects, as the operational state of the fuel cell, one of atemperature of the fuel cell, an exhaust gas temperature in a fuel gassystem, and an exhaust gas temperature in an oxidative gas system, andthe diagnostic portion diagnoses the state of the fuel cell based on oneof the temperature of the fuel cell, the exhaust gas temperature in thefuel gas system, and the exhaust gas temperature in the oxidative gassystem, which is detected.
 11. The diagnostic apparatus for a fuel cellaccording to claim 1, wherein the diagnostic portion determines thatthere is a mechanical failure or deterioration due to a secular changewhen an output voltage of the fuel cell is less than a predeterminedvalue in a case where the fuel cell is operated according to the atleast one predetermined operation pattern.
 12. The diagnostic apparatusfor a fuel cell according to claim 1, which diagnoses a state of a fuelcell installed in a moving object as a power source, wherein theoperation device includes a device installed in the moving object, theoperational state detecting portion includes a moving object detectingportion which is installed in the moving object, and which detects astate as the operational state of the fuel cell, the device controlportion can be connected to a control system which is installed in themoving object for controlling an operation of the fuel cell, andcontrols the operation device by giving an instruction to the controlsystem, and the operation device includes a power adjusting portionwhich adjusts power generated by the fuel cell.
 13. The diagnosticapparatus for a fuel cell according to claim 12, wherein the poweradjusting portion is connected to an output terminal of the fuel cell,and adjusts the power generated by the fuel cell by absorbing orconsuming the power.
 14. The diagnostic apparatus for a fuel cellaccording to claim 12, further comprising: a fuel gas supply portionwhich supplies the fuel cell with a fuel gas that is used for powergeneration of the fuel cell, instead of a fuel gas supply system whichis installed in the moving object for supplying the fuel cell with thefuel gas.
 15. The diagnostic apparatus for a fuel cell according toclaim 12, further comprising: a cooling portion which cools the fuelcell, instead of a cooling system which is installed in the movingobject for cooling the fuel cell.
 16. A diagnostic method for a fuelcell, which is a method for diagnosing a state of the fuel cell,includes the steps of: (a) operating the fuel cell according to at leastone predetermined operation pattern; (b) detecting a change in anoperational state of the fuel cell corresponding to each of theoperation patterns when the fuel cell is operated according to the atleast one predetermined operation pattern; and (c) diagnosing the stateof the fuel cell based on the detected change in the operational stateand the at least one predetermined operation pattern.
 17. The diagnosticmethod for a fuel cell according to claim 16, wherein in the step (c),the state of the fuel cell is diagnosed by comparing the change in theoperational state of the fuel cell corresponding to each of theoperation patterns, which is detected when the fuel cell is operatedaccording to the at least one predetermined operation pattern, with achange in a normal operational state of the fuel cell corresponding toeach of the operation patterns, which is detected when the fuel cellthat normally functions is operated according to the at least onepredetermined operation pattern.
 18. The diagnostic method for a fuelcell according to claim 16, wherein in the step (a), the fuel cell isoperated according to one of a predetermined pattern ofincreasing/decreasing a flow amount of a fuel gas and/or an oxidativegas that is supplied to the fuel cell, a predetermined pattern ofincreasing/decreasing a supply pressure, and a predetermined pattern ofincreasing/decreasing a degree of humidification, as one of theoperation patterns.
 19. The diagnostic method for a fuel cell accordingto claim 16, wherein in the step (b), one of i) an output current and anoutput voltage of the fuel cell, ii) an interterminal voltage or a cellvoltage when the fuel cell is in an open state, iii) an internalresistance of the fuel cell; iv) a temperature of the fuel cell, v) anexhaust gas temperature in a fuel gas system of the fuel cell, vi) andan exhaust gas temperature in an oxidative gas system of the fuel cellis detected as the operational state.